1. Field of the Invention
The present invention relates to an electrically heated nozzle assembly for use in a metal die casting process.
2. Prior Art
In the die casting of metals, it has been known in the art to place a nozzle between a die and an apparatus for injecting molten metal into the die. The use of such a nozzle is discussed briefly in Chapter 3 of Pressure Die Casting Part One by B. Upton, published in 1982 by Pergamon Press Limited. However, prior art die casting nozzles lacked the ability to achieve a consistent temperature throughout the nozzle, and sometimes the molten metal would begin to solidify within such a prior art nozzle, thus restricting flow.
The prior art die-casting nozzles were usually heated externally with a blow torch, which caused hot spots within the nozzle, and which created external environmental problems such as creating a fire hazard and heating up the work area to the extent that it became uncomfortable for the machine operator.
One effort has been made by DME to market an electrically heated nozzle for use in die-casting, but the previous electric nozzle design, which involved using a ceramic band heater externally of the nozzle, has been withdrawn from the market.
It would be advantageous to precisely control the temperature within a die-casting nozzle to an optimal temperature as an aid to process control. Simplicity of design and servicing are also highly beneficial in industrial equipment.
A brief discussion of some patents for heated nozzles and other fluid heaters in technologies other than die casting follows.
Krohn et al., U.S. Pat. No. 3,835,924, discloses a high pressure heater for paint including a cylindrical core having a continuous spiral groove in a surface of the cylinder. An electric heating element is axially centrally disposed in the core and paint flows through the spiral groove to be heated by the heating element.
Osuna-Diaz, U.S. Pat. No. 4,196,855, discloses a machine nozzle attached to the barrel of an injection molding machine for use in plastic injection molding. The nozzle includes a body having a central passage therein, the body surrounded by a coiled electric heater extending substantially the full length thereof. A cover surrounds the heater, and a removable retainer is attached to the end of the body.
Lehrke, U.S. Pat. No. 4,501,952, discloses a fluid heater, particularly for heating paint, lacquers, finishes and other spray coating material. The heater of Lehrke includes an elongated hollow tube adapted to be inserted into a fluid flow line for fluid flow through the tube. An electric resistance heater is axially centrally disposed within the tube, the heater being surrounded by a helical coil-shaped passage which creates a helical flow path through the tube around the heater.
Although the prior art provides a variety of heated tubes for various uses, a need still exists in the metal die casting industry for a heated nozzle which is designed and constructed specifically for metal die casting, and for a heated nozzle assembly including a control mechanism for controlling the nozzle to a desired temperature to control process variability.